Aircraft with retractable landing gear must provide a dedicated system as a back-up to the aircraft's normal on-board landing gear retraction/extension system which will allow the aircraft's landing gear to be extended in an emergency situation (e.g., a situation in which the landing gear fails to be deployed into an extended condition by the normal on-board gear extension system due to a component failure). In general, all emergency back-up gear extension systems should be both simple to operate and completely segregated from the normal on-board landing gear actuation systems.
There are several types of emergency back-up gear extension systems that are conventionally available for aircraft, including for example, electrically actuated systems, hydraulically actuated systems, spring actuation mechanisms, and energy transmission systems whereby the energy to release the landing gear is provided only by the pilot.
Another type of emergency landing gear deployment systems includes those that rely on gravity free-fall of the landing gear assemblies. For example, in those aircraft with relatively heavy landing gear assemblies (including for example the landing gear struts and associated structural components as well as the landing wheel assemblies), emergency landing gear deployment systems have been developed which allow the landing gear to essentially “free fall” under the influence of gravity from their retracted and up-locked position to an extended and down-locked position. However a free-fall emergency landing gear actuation system becomes more complex when landing gear doors have dedicated door actuators. In such a case, during normal operation, the selector valve for the gear position controls the gear door opening and closing separately from the landing gear extension. However, in a free fall operation, the gear door valve is in an off condition and thus the gear doors are not allowed to free-fall along with the landing gear assembly. Instead, the gear doors are forced open by contact with the gear assemblies when in free-fall. In order to ensure that the gear doors do not jam the emergency extension of the free-falling landing gear, some additional structure and/or device is typically necessary to allow the gear to open in an emergency gear deployment situation. For this reason, gear doors associated with conventional free-fall emergency gear deployment systems may be provided with low friction skid plates or other means by which contact with the landing gear tires during free-fall gravity extension of the landing gear will forcibly move the gear doors to an opened state yet minimize the possibility that the doors will jam the gear extension sequence.
In some cases, however, the additional structure and/or devices to ensure gear door opening during landing gear free-fall are not effective, for example, in those situations where the kinematics of the gear door do not have harmonic movement in the same direction as the associated landing gear. In such a situation, there is a real risk that the landing gear will become jammed with its associated gear door—an event that is of course unacceptable. The design of the gear doors is thus usually sacrificed in order to create the required harmonic movement with the associated landing gear in an effort to eliminate the risk of the doors jamming the landing gear movement during emergency free-fall extension.
What has been needed in this art, therefore, are emergency gear actuation systems for aircraft landing gear which allows the landing gear doors to be opened with little or no physical interference with the associated landing gear assembly during emergency gravity free-fall landing gear deployment. It is toward providing such a need that the embodiments of the present invention are directed.